1. Technical Field
The present invention relates to a control device for lighting a lamp and detecting a breakage of the lamp, and in particular to a control device for lighting a lamp composed of a light emitting diode (LED) and detecting a breakage of the lamp.
2. Related Art
If a vehicle lamp, such as a front light, a direction indicator or a stop lamp, is not lighted due to the breakage thereof, the driver has trouble with driving at night or cannot show his/her intention of changing a running direction of the vehicle or stopping it to other surrounding vehicles. In order to avoid such troubles, techniques for detecting a breakage of a vehicle light have been contemplated so far. For example, JP 08-332897 A discloses a technique for detecting respective voltages of lighting lamps connected to a control unit, and determining which lamp is broken based on variations in the resistances of the lamps.
On the other hand, lately, LEDs have been increasingly used as light sources for lamps provided in vehicles or facilities, because of their low electricity consumption.
For example, JP 2010-105590 A discloses an LED breakage detection device that aims to detect a breakage of an LED without lighting the LED. The LED breakage detection device is configured to supply an LED with a pulse signal having a pulse duration that is set so as not to light the LED and to detect presence or absence of a breakage of the LED while the pulse signal is being supplied to the LED.
JP 2011-98620 A discloses a breakage detection device that aims to detect a breakage of a luminous element stably with a simple configuration. The breakage detection device includes: first and second resistance elements connected in series; third and fourth resistance elements connected in series and having one end connected to a signal input terminal from a vehicle side and the other end connected to the collector of an NPN transistor; a PNP transistor having the base connected to a connection node of the third and fourth resistance elements and the emitter connected to the signal input terminal; a diode having the anode connected to the collector of the PNP transistor; a fifth resistance element having one end connected to the cathode of the diode and the other end connected to the ground terminal; and a capacitative element having one end connected to the cathode of the diode and the other end connected to the ground terminal.
JP 2010-287601 A discloses a luminous element driver device that aims to reliably and readily detect a short or breakage failure of luminous elements used for a backlight source of LCD-TV or the like. The luminous element driver device monitors respective voltages at connection nodes of a driver circuit and luminous element arrays, each of which has luminous elements connected in series, and includes maximum and minimal detection units that detect the maximum and minimal ones of the monitored voltages, respectively. Further, the luminous element driver device compares a difference between the maximum and minimal voltages with a predetermined reference voltage, thereby detecting a short or breakage of each luminous element.
JP 2008-168706 A discloses a light source unit group lighting device that aims to determine a failure of each LED in a turn lamp. When all LED units are in a non-broken state, the light source unit group lighting device lights all the LED units in response to lighting instruction signals inputted intermittently. Meanwhile, when at least one of the LED units is in a broken state, the light source unit group lighting device lights another non-broken LED unit during a certain time period in response to the first one of lighting instruction signals inputted intermittently, and then lights it out. Subsequently, the light source unit group lighting device maintains all the LED units in a light-out state upon inputs of the second and subsequent ones of the lighting instruction signals.
However, it is more desirable to detect a breakage of an LED without making a user aware of the detection.